1. Field of Invention
The present invention relates to a method for diagnosing an exhaust gas recirculation (EGR) system, and more particularly, to a method for diagnosing an EGR system capable of diagnosing a fault of the EGR system by a temperature sensor installed at an outlet side of an EGR line.
2. Description of Related Art
Generally, a basic purpose of using an exhaust gas recirculation (EGR) system is to decrease NOx exhausted from an engine. When exhaust gas exhausted from the engine is again circulated to an intake port, oxygen required for combustion is relatively decreased, such that NOx is decreased.
However, when a flow of EGR gas is decreased due to a fault of the EGR system, an exhaust amount of NOx exhausted at the time of combustion is increased, which is an on-board diagnostics (OBD) rule and needs to be monitored.
Meanwhile, in a EURO4 commercial diesel engine, a fault of the EGR system has been diagnosed using an air mass flow (AMF) sensor.
That is, when an intake amount is measured by the AMF sensor, a difference value between the measured intake amount and an expectation intake amount mapped thereto is calculated. In addition, the calculated difference value is compared with a reference intake amount, and a fault diagnosis that an EGR gas amount is insufficient or excessive is performed when the different value does not satisfy the reference intake amount.
However, in the above-mentioned method for diagnosing a fault, the fault of the EGR system is indirectly diagnosed by the AMF sensor. Therefore, when the AMF sensor is deteriorated or a fault is generated in the AMF sensor, an erroneous diagnosis that the entire EGR system is problematic is performed.
Further, in the AMF sensor, a deviation of a sensed value occurs due to aging of the sensor such as attachment of foreign materials in exhaust gas to the AMF sensor, a difference in an intake layout according to a kind of vehicle (a difference in an air mass flow shape) occurs, a measurement error by the AMF sensor increases by a driving surrounding environment of a driver, or the like.
Meanwhile, according to the related art, Korean Patent Laid-Open Publication No. 10-2011-0003953 entitled “Structure and Method for Controlling EGR Valve of Engine” has been disclosed.
However, even in this scheme, an EGR flow of an EGR system is adjusted using the AMF sensor, such that an error occurs when the AMF sensor is deteriorated.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.